Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1: Base Functions, Connectivity, and Routing

28 Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1 - Base Functions, Connectivity, and Routing

When considering allowing applications to use their own set of statements, it is important to

set up a DEFAULTTCPIPDATA file, so the environment will provide the application owners

with the possibility of using their own settings, while it will maintain the basic settings defined

for those who do not want to define their own definitions.

2.3.2 Using the Resolver address space in a multiple stack environment

When implementing a Resolver address space with global settings in a multiple stack

environment, we must be very careful. The Resolver address space is a single process within

the z/OS LPAR, which means the global environment (GLOBALTCPIPDATA) statements will

have an impact on all stacks within the z/OS LPAR.

What should be taken into consideration when deciding whether to use GLOBALTCPIPDATA

is to verify that all stacks will use common Resolver statements, such as NameServer and

domainorigin. If they cannot use common Resolver statements, then you must use distinct

TCPIP.DATA data sets for setting up a DEFAULTTCPIPDATA file to define a default TCP/IP

stack for applications that do not define their own Resolver statements.

In our scenario, we will implement a global environment defining a common set of

statements. This will allow each stack to use its own TCPIP.DATA data set to define the local

environment and will create a default TCPIP.DATA defining stack TCPIPA as the default

TCPIPJOBNAME statement (see Figure 2-6).

Figure 2-6 Multiple stacks with global Resolver environment

Important: In some Resolver environments, the use of the trace functions (such as

SockDebug or TraceResolver) may affect performance. Therefore, we recommend using

the method described in “CTRACE - RESOLVER (SYSTCPRE)” on page 46.

Resolver

TCPIPA

Stack A

TCPIPB

Stack B

LPAR30

GLOBALTCPIPDATA('TCPIPA.TCPPARMS(GLOBAL)')

DEFAULTTCPIPDATA('TCPIPA.TCPPARMS(DEFAULT)')

GLOBALIPNODES (’TCPIPA.TCPPARMS(IPNODES)’)

COMMONSEARCH

RSSETUP

//RESOLVER PROC PARMS='CTRACE(CTIRES00)'

//EZBREINI EXEC PGM=EZBREINI,REGION=0M,TIME=1440,PARM=&PARMS

//SETUP DD DSN=USER1.TCPCS.TCPPARMS(RSSETUP),DISP=SHR,FREE=CLOSE

TCPIPA.TCPPARMS(GLOBAL):

Nameserver 10.1.1.1

Domain itso.ibm.com

Resolvevia UDP

...

TCPIPB.TCPPARMS(DATAB30):

Hostname SC30B

TCPIPJobname TCPIPB

...

TCPIPA.TCPPARMS(DATAA30):

Hostname SC30A

TCPIPJobname TCPIPA

...

TCPIPA.TCPPARMS(DEFAULT):

Hostname SC30

TCPIPJobname TCPIPA

Chapter 2. The Resolver 29

Using local settings in a multiple stack environment

When designing a multiple stack scenario, it is important to check each application that will be

used and how it will be implemented in the environment. Each type of application has its own

relationship with a TCP/IP stack, for example:

򐂰 A native TCP/IP sockets program will always use one stack only—by default the stack that

is identified in the TCPIPJOBNAME option in the chosen Resolver configuration file.

However, the stack can also be chosen via the program configuration and API calls to

associate the program with a chosen stack, as shown in Figure 2-7.

Figure 2-7 Native TCP/IP applications in a multiple stack environment

򐂰 Applications using UNIX System Server callable APIs or LE C/C++ sockets APIs can be

implemented using a generic bind to open the same port in all TCP/IP stacks. By doing so,

the application will accept incoming connections or UDP datagrams over any interface of

all connected stacks, as shown in Figure 2-8 on page 30.

Outbound connections or UDP datagrams are processed by the C-INET pre-router, and

the stack with the best route to the destination is chosen.

When using a generic bind, the server port number must be reserved in all stacks. If one

has it reserved to another address space, the bind() call fails.

When using the generic bind, it does not matter if the chosen Resolver configuration file

has a TCPIPJOBNAME; it is not used when the server is a pure generic server.

Inbound Outbound

Native MVS

Socket

Program

X

TCPA TCPB

TCPC

YZV

C-INET

BPX Callable Sockets

Pre-routing Table

TCPIPJobname

TCPB

30 Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1 - Base Functions, Connectivity, and Routing

Figure 2-8 UNIX System Server callable APIs or LE C/C++ sockets APIs using Generic bind in a

multiple stack environment

򐂰 Applications using UNIX System Server callable APIs or LE C/C++ sockets APIs can also

use a specific bind to open a socket. A bind-specific server socket will only receive

connections from the stack that owns the IP address to which the socket is bound.

Outbound connections or UDP datagrams will be handled by the stack that offers the best

route to the destination IP address, as shown in Figure 2-9.

Figure 2-9 UNIX System Server callable APIs or LE C/C++ sockets APIs using specific bind in a

multiple stack environment

Inbound Outbound

socket( )

bind(8001, 0)

listen( )

X

TCPA TCPB

TCPC

YZV

C-INET

BPX Callable Sockets

Pre-routing Table

Inbound Outbound

socket( )

bind(8001, Y)

listen( )

X

TCPA TCPB

TCPC

YZV

C-INET

BPX Callable Sockets

Pre-routing Table

Application-specific

Configuration Data